Brachipods Flashcards
“Brachiopoda” literally means “arm-foot” why?
Originally, the bi-valved brachiopods were thought to be related to the bi-valved mollusks, which have a muscular organ called a “foot”. The brachiopod lophophore, which is used in filter-feeding, has two arm-like branches, which early biologist erroneously confused with the “foot” of mollusks. Because brachiopods share the “lophophore” (feeding structure with tentacles) with bryozoans, the braciopods in fact are much more closely related to the tiny, colonial bryozoans than they are to mollusks!
Phylum Brachiopoda:
bivalved animals with a lophophore & a pedicle
What are the two classes of Brachiopoda?
Class Inarticulata and Class Articulata
Class Inarticulata:
(brachiopods without a hinge; Lower Cambrian to Recent) - Four Orders
Class Inarticulata Geologic Range:
Lower Cambrian to Recent
Class Articulata:
brachiopods with a hinge; Lower Cambrian to Recent - Six Orders
Class Articulata Geologic Range:
Lower Cambrian to Recent
Lophophore:
Distinctive feeding structure inside the brachiopod shell, consisting of two arm-like “brachia” that bear cilia, which beat back and forth in the water to create microcurrents and strain suspended food particles from the water; attached to inside of brachial valve.
Brachia:
Two arm-like branches of the lophophore; attached to brachial valve.
Pedicle:
Tough, fleshy stalk attached to pedicle valve and extending from the beak of the shell. (Brachiopod)
Mantle:
Thin sheet of tissue that lines the inside of the brachiopod shell
Periostracum:
Brown, scaley, organic “skin” coating the outside of some brachiopod shells.
Adductor muscles:
Muscles that close the two valves of the shell.
Diductor muscles:
Muscles that open the two valves of the shell (only found in Articulates).
Pedicle adjustor muscles:
Muscles that move the main body mass around at the end of the pedicle (only found in Articulates).
Oblique muscles:
Muscles that rotate and/or slide the two valves with respect to one another (only found in Inarticulates).
Valves:
The two main parts of the brachiopod shell
Brachial valve:
“Dorsal” valve, to which the lophopore is attached
Pedicle valve;
“Ventral” valve, to which the pedicle is attached.
Commissure:
Broad “anterior” margin of the shell opposite the pedicle and hinge.
Beak:
Pointed “posterior” end of the shell, from which the pedicle protrudes.
Hinge:
Structure at the beak that holds the two valves together and allows them to open and close in an articulated fashion (only found in Articulates).
Tooth & socket structure:
Small projections & corresponding pits on inside of the beak.
Interarea:
Outside pt of the shell located between the two pointed parts of the beak.
Pedicle Opening:
Hole or notch in the beak to allow the pedicle to protrude from the shell.
Foramen:
Round hole on the pedicle valve.
Delthyrium:
“V”-shaped notch on pedicle valve.
Notothyrium:
“V”-shaped notch on brachial valve.
Brachidium:
Calcareous lophophore support on insde of bracial valve (only in Articulates)
Crura:
Simple, forked brachidium in Rhynchonellids
Spiralium:
Ornate, coiled brachidium in Spiriferids
Loop:
Curved, lasso-like brachidium in Terebratulids
Fold:
Broad central ridge (usually on brachial valve) extending from beak to commissure.
Sulcus:
Deep central groove (usually on pedicle valve) corresponding to the fold.
Class Inarticulata:
brachiopods without a hinge; shell may be composed of calcite, calcium phosphate, or layered or unlayered chitinophosphate
Orders of Class Inarticulata:
Paterinida, Obolellida, Lingulida, Acrotretida
Order Paterinida:
Cambrian to Ordovician, Tiny (<5mm) brachiopods with a biconvex, phosphatic shell that has both a delthyrium and notothyrium; not very important
Order Obolellida:
Cambrian Only, Small (usually <1cm) brachiopods with a biconvex, calcite shell that has a tiny, slit-like pedicle foramen; not very important
Order Lingulida:
Cambrian to Recent: Circular or elongate brachiopods (up to 5 cm long) with a biconvex, chitinophosphatic shell; moderately important as fossils
Order Acrotretida:
Cambrian to Recent: Tiny (usually <2mm) brachiopods with a flattened, circular, calcite or phosphatic shell; no pedicle; some forms are attached by cementing one valve to a rock or another shell; somewhat important as fossils.
Class Articulata:
Brachiopods with a hinge; shell always composed of layered calcite
Order Orthida:
Cambrian to Permian, Inequivalved shell, which may be biconvex, concavoconvex, plano-convex or convexo-concave, commonly with fine to coarse radiating ribs “costae”, pedicle protrudes through notothyrium and delthyrium; no brachidium; usually impunctate, but some forms are punctate; important as fossils.
Order Pentamerida:
Cambrian to Devonian, Biconvex shell, usually with a smooth surface; characterized by a trough-shaped or spoon-like structure (“spondylium”) inside the pedicle valve, to which the pedicle is attached; simple rod-like or blade-like lophophore supports on brachial valve; always impunctate; not very important.
Order Strophomenida:
Ordovician to Triassic, Grossly inequivalved shell, usually panlo-convex or concavo-convex, commonly with radiating ribs and/or concentric growth lines; characterized by a very wide hingeline and inflated pedicle valve; sometimes a pedicle foramen, or else no pedicle opening at all; sometimes there are long spines on pedicle valve; wide variety of spiralled lophophore supports; always pseudopunctate; this is the most diverse brachiopd order, so it is very important.
Order Rhynchonellida:
Ordovician to Recent; Biconvex shell with a short hingeline and prominent beak; characterized by a strongly corrugated (“plicate”) shell with a very priminent fold and sulcus; pedicle protrudes throug a delthyrium; simple, forked brachidium (“crura”); usually impunctate, but some forms are punctate; important as fossils.
Order Spiriferida:
Ordovician to Jurassic: Very wide, biconvex shell with a long hingeline and short beak-to-commissure distance; characterized by its “wing-like appearance; promient fold and sulcus; pedicle protrudes through a delthyrium or pedicle foramen; thightly spiralled brachidium (“spiralium”); may be impunctate or punctate; important as fossils.
Order Terebratulida:
Devonian to Recent, Biconvex shell with a very short hingleine characterized by its “Aladdin’s Lam;” appearance; shell surface smooth or finely ribbed; pedicle usually protrudes through a pedicle foramen; loop-shaped brachidium; always punctate; important as fossils.
Brachipod shell geometries:
Biconvex
Concavo-Convex
Convexo-concave
Plano-convex
Biconvex:
Both valves convex
Concavo-convex:
Brachial valve concave, and pedicle valve convex
Convexo-concave:
Brachial valve convex, and pedicle valve concave.
Plano-convex:
Brachial valve planar, and pedicle valve convex
Organic lining of brachiopod shells:
Periostracum, Mantle
Periostracum:
Tough, brown “skin”, which covers the outside of the shell.
Mantle:
Soft tissue, which lines the inside of the valves and secretes the shell material.
Inarticulate brachiopod shell composition:
1) Pure chitin, layered
2) Chitinophosphatic, unlayered
3) Chitinophosphatic, layered
4) Pure calcite, unlayered
Articulate brachiopod shell composition:
1) Pure calcite, layered (all articulate brachiopods)
Layered ultrastructure of Articulate shells:
Primary “Lamellar” layer (found in all Articulates)
Secondary “Fibrous” layer (found in all Articulates)
Secondary “Prismatic” layer (only found in some Pentamerids & some Spiriferids)
Punctation structure of Aritculate shells:
1) Impunctate
2) Punctate
3) Pseudopunctate
Impunctate:
No punctae in the shell (found in all Pentamerids; found in the earliest Orthids, Rhynchonellids & Spiriferids)
Punctate:
Punctae (tubular perforations) extending through the fibrous and lamellar layers (found in later Orthids, Rhynchonellids & Spiriferids; found in all Terebratulids)
Pseudopunctate:
Pseudopunctae (rods of sollid calcite) in the fibrous layer (found in all Stromphomenids
Draw each punctation structure of Articulate shells:
See 9d
Evolutionary relationships of Brachiopods:
1) Phylum Brachiopoda may (or may not) be “polyphyletic”, i.e., the two classes are so dissimilar that it is possible they may have evolved independently of one another
2) Inarticulates: Since all four inarticulate brachiopod orders appeared about the same time in the Early Cambrian, any common ancestor would have been a Precambrian (presumably shell-less) form that is not preserved, so the evolutionary relationships of the inarticulate orders are unclear
3) Articulates: The six articulate brachiopod orders are evolutionarily related, and it appears that they all stemmed ultimately from the orthids that first appeared in the Early Cambrian
Life Habits of Brachiopods:
- Brachiopds are/well all sessile, benthic, filter feeders
- Almost all are/were epifaunal (living on rather than in the sea floor), except for some deep-burrowing lingulids and shallow-burrowing strophomenids.
- Most articulate brachiopods are/were firmly attached to hard substrates with the pedicle
Paleoecology of Brachiopods:
- Almost entirely normal marine, except for some lingulids that can tolerate variable salinity.
- Mainly live in shallow-marine habitats
- Most Paleozoic brachiopods preferred warm, clear, tropical waters
- Today, brachiopds are most common on cool, mid-latitude waters.
What is the taxonomic degradation of Brachiopods?
See Onesheet
